1. Field of the Invention
The present invention belongs to a technical field of a vehicle control system that performs control of a vehicle based on an auxiliary machine motive power.
2. Description of the Related Art
Technology described in, for example, Japanese Patent Laid-open No. Hei-175517 is well known as a vehicle control system of this type. This prior publication discloses a technique for obtaining an intake pressure set value from a detected heat load to calculate a required driving torque for a variable displacement compressor, thereby using the calculated torque for controlling an engine.
Specifically, in this prior art, a heat load calculation means, a required driving torque calculation means for a compressor, and an idle-up control means are used for calculating a torque that is a motive power of an auxiliary machine, and this torque is used for idle control of an engine.
Incidentally, in the above-described prior art, it is presumable that the required driving torque calculation means for a compressor performs calculation processing by an electronic device, and specifically, this electronic device is conceivable to be an airconditioning control ECU or an engine control ECU. Further, although there is no electronic device specified for the idle-up control means either, it is conceivable to be an engine control ECU.
Specifically, when the torque calculation means is the airconditioning control ECU, it needs to communicate with the engine control ECU, and when the torque calculation means is the engine control ECU, it is conceivable that the torque calculation means performs an idle control, which is an engine control, by communicating signals within the engine control ECU.
Here, if the torque calculation means is located inside the engine control ECU, a processing routine for calculating the required driving torque is needed for processing inside the engine control ECU. Since the engine control is generally performed at quite high speed, in order to perform a processing routine with a long processing time in the engine control, a CPU (central processing unit) that is capable of processing at higher speed is required in the engine control ECU, which causes a problem of making the engine control ECU expensive.
Meanwhile, if the torque calculation means is located inside the airconditioning control ECU, the reliability of the airconditioning control ECU becomes relatively lower than that of the engine control ECU from a viewpoint of manufacturing cost reduction. Accordingly, in case of failure or malfunction of the airconditioning control ECU, false torque data are communicated to the engine control ECU. In other words, if the torque data are larger than true values, fuel efficiency of the engine decreases, or if the torque data are smaller than the true values, it can cause a phenomenon called engine stall, which causes a problem of increasing the danger in driving a vehicle.